Structural and electrochemical corrosion properties of plasma-sprayed CoCrFeNiMo HEA coating in corrosive solutions

A CoCrFeNiMo high-entropy alloy (HEA) coating was prepared on Ti6Al4V alloy by plasma spraying technique. The microstructure and phases of the obtained coating were analysed using an ultra-depth-of-field microscope and X-ray diffraction, respectively. The electrochemical corrosion properties of CoCrFeNiMo HEA coating in 3.5% NaCl, 0.1 M H2SO4 and 0.1 M NaOH solutions were comparatively evaluated using an electrochemical workstation, and the corrosion mechanisms were also discussed by the corrosion models. The results show that the CoCrFeNiMo HEA coating is mainly a solid solution structure of face-centered cubic, which forms mechanical bonding at the coating interface. The charge transfer resistance Rct of 597 × 1016 μA·cm–2 in 0.1 M H2SO4 solution is the highest and the corrosion current density icorr of 4.203 × 10–7 μA·cm–2 also presents the lowest among the three kinds of corrosive solutions, which shows the highest electrochemical corrosion resistance. As a result, the sequence of corrosion resistance is in 0.1 M H2SO4 solution > in 3.5% NaCl solution > in 0.1 M NaOH solution, in which the corrosion resistance is further improved by the passive film on the CoCrFeNiMo HEA coating.